Bath for galvanic deposition of gold and gold alloys

ABSTRACT

Galvanic baths are provided for the deposition of gold or gold alloy coatings, such baths containing in combination aldehyde and nitrogen compounds with arsenic compounds.

United States Patent 1 Dettke et a1.

[ BATH FOR GALVANIC DEPOSITION OF GOLD AND GOLD ALLOYS [76] Inventors:Manfred Dettke, Angersburgallee, 1

Berlin 19; Karl-Hans Fuchs, Holderlinstrasse 1 1, 7015 Korntal; RolfLudwig, Neve Kantstrasse 21/22, 1 Berlin 19, all of Germany [22] Filed:Aug. 29, 1973 21 Appl. No.: 394,959

[30] Foreign Application Priority Data Sept. 6, 1972 Germany 2244434[52] US. Cl. 204/43 G; 204/44; 204/46 G [51] Int. Cl C23b 5/28; C23b5/42; C231) 5/46 [58] Field of Search 204/46 G, 43 G, 44; 106/1 [451Apr. 15, 1975 Primary Examiner-G. L. Kaplan Attorney, Agent, orFirm-Joseph F. Padlon 57 ABSTRACT Galvanic baths are provided for thedeposition of gold or gold alloy coatings, such baths containing incombination aldehyde and nitrogen compounds with arsenic compounds.

5 Claims, No Drawings BATH FOR GALVANIC DEPOSITION OF GOLD AND GOLDALLOYS The invention relates to a bath for the galvanic deposition ofgold coatings and gold alloy coatings, containing a combination oforganic compounds on a base of aldehydes and nitrogen compounds witharsenic compounds.

The use of nitrogen-containing compounds, such as hydrazine andderivatives thereof, in gold electrolytes for reducing the internalstresses of the coatings deposited therefrom is known, of, German Pat.Nos. 1,215,467, 1,218,248 and 1,222,347.

It is further known that soluble arsenic compounds are added to goldelectrolytes in order thereby to achieve an improved luster of the goldcoatings. Cf., German Nos. 2,042,127, 1,621,172 and 1,621,068.

An essential disadvantage of these electrolytes, however, is that theirsmoothing or leveling action is not satisfactory.

It is, therefore, an object of the present invention to avoid thedisadvantages of the known electrolytes and to provide galvanic bathsfrom which smooth coatings of gold and the alloys can be deposited.

This is achieved according to the present invention by providing a bathwhich is characterized by a content of t A. at least one compound of thegeneral formula R CHO in which R signifies hydrogen, methyl or the group-CHO, or one of its addition compounds and B. at least one compound ofthe general formula in which the radicals R are identical or differentand represent hydrogen, possibly alkyl substituted by hydroxy groupswith preferably 1 to 4 carbon atoms or aryl and R alkylidene radicalswith preferably 1 to 5 carbon atoms, in and n being or representingintegers from 1 to 3, or one of their salts and C. at least one alkalisalt of arsenic or arsenous acid,

such as sodium and potassium arsenite or sodium and potassium arsenate,

1n the general formula under (B) above, the radicals R signify forexample methyl, ethyl, propyl, butyl or isobutyl, and the radicals R,signify methylene, ethylidene, propylidene, butylidene, pentylidene andthe like, the alkyl radicals being preferably substituted with up to 2hydroxy groups.

The components (A), (B) and (C) seem to influence each othersynergistically in the bath, for when used alone they are completelyineffective.

The concentrations required for a high-gloss gold deposition or achromatic gold alloy deposition are, for the aldehydes, i.e., componentA, about 0.005 to 50 g/liter, for the nitrogen compounds, i.e.,component B, about 0.1 to 50 g/liter, and for the arsenic compounds,i.e., component C, about 0.001 to g/liter.

As aldehyde components there are suitable preferably formaldehyde,acetaldehyde and glyoxal, which can be used per se or in the form oftheir addition compounds, i.e., as bisulfites.

Nitrogen compounds that are especially suitable, are hydrazine or methylhydrazine, which are to be used according to invention either bythemselves or in the form of their salts, such as the chlorides orsulfates, or alone or in a mixture with one another. In addition,prropyl hydrazine as well as phenyl hydrazine and the substitutionproducts thereof and their salts have proved to be suitable.

Further nitrogen compounds that may be used according to the inventionare, for example, N-(3-propy1- 5 l,2-diol)-diethylene triamine,triethylene tetramine,

ethylene diamine, diethylene triamine, triethylenetetramine andtetraethylene pentamine, of which the first two in particular have beenfound to be very favorable with respect to their smoothing action.

Also, these compounds can be used by themselves as such, as well as inthe form of their salts, for example, the chlorides or acetates.

Suitable arsenic compounds that are effective are the alkali salts ofarsenic and arsenous acid, such as sodium and potassium arsenate orarsenite.

It is understood that the components (A), (B) and (C) may be used eitherby themselves alone, or in the form of their mixtures.

As a bath, there is generally used an aqueous solution which contains awater-soluble gold salt, preferably a complex compound of gold, inparticular potassium dicyanoaurate (I), in concentrations of about 1 to50 g/liter.

1f gold alloy coatings are to be deposited, there are added to the baththe alloy metals silver, copper, zinc, cadmium, manganese, cobalt,nickel, palladium, indium, antimony 'or tin, in the form of theirwatersoluble compounds, preferably in the form of the complex compounds,such as the chelate or the cyano complexes, in total concentrations ofabout 0.01 to 200 g/liter. Depending on whether binary, ternary orquaternary alloy coatings are intended, corresponding mixtures of themetal compounds are used.

It has been found particularly appropriate if the bath contains boricacid and a polyvalent alcohol, preferably ethylene glycol, namely moreparticularly in a ratio by weight of about 1:1 to 1:2 and in aconcentration of about to 200 g/liter of boric acid or of about 10 to2000 g/liter of alcohol.

As additional additives, the bath may contain common conducting salts,for example ammonium sulfate or alkali salts of sulfuric acid, nitricacid or hydrochloric acid, pH-regulating substances, appropriately theorganic and/or inorganic buffer mixtures commonly used for this purposesuch as, mixtures of citric acid and potassium citrate or sodiumhydrophosphate and sodium dihydrophosphate as well as surface-activesubstances, such as ethylhexylsu lfate and N- ethoxyhexylamine.

The pH value of the bath may .be from about 5 to 10, preferably 6.8 to7.5. It is operated appropriately at temperatures of about to 70 C,preferably at temperatures between to C, current densities from about0.1 to 5 amp.dm being used.

The bath according to the invention is suitable in particular for thegalvanic deposition of high-gloss gold coatings and chromatic gold alloycoatings with excellent smoothing appearance.

Another advantage of the invention consists in the extraordinaryadhesion of the coatings, which, surprisingly, far exceeds that of thecoatings produced by the usual, known methods. Thus, for example, eventhe lead containing brass alloy, which is very difficult to galvanize orplate, can be gold plated directly without the previous deposition of anintermediate layer by means of the bath according to this inventionresulting in a substantial saving of material and time.

It should be stressed further that the bath of the invention permits theuse of high current densities and at good current efficiency shorterexposure times, whence special advantages result for the practice.

The following examples will illustrate the invention, without limitationthereof.

pH value: 6.8 which is adjusted with sulfuric acid Applicable currentdensity: from 0.1 to maximum 2.0 amp.dm Temperature: to 70 C The rate ofdeposition at l ampldm z 1 micron in 4 minutes.

This electrolyte composition according to the invention is suitable forthe deposition of nearly 24 carat gold. The coatings deposited from thiselectrolyte are of high luster, saturated gold color, and have ahardness of about 170 microvickers.

With the electrolyte, lead containing brass can be proviced, without anintermediate layer, with a gold coating which is of high luster fromabout 8 micron on.

EXAMPLE 2 g/liter Potassium dicyanoaurate (l), K(Au(CN) 12.0 Ammoniumsulfate, (NHQ SO 70.0 Boric acid, H 30 40.0 Ethylene glycol, HOCH -CH OH80.0 Copper sulfate, CuSO '5 H O 8.0 Ethylene diamine tetraceticaciddipotassium salt 9.5 Formaldehyde, CH O 5.0 Hydrazine hydrate N H 'H O12.0 Sodium arsenite, Na ASO 0.045

By means of this electrolyte, about 18 carat coatings can be deposited,which have the color of rolled gold. The coatings are of high gloss andtarnish resistant.

pH value: 8.0

Applicable current density: From 0.1 to 1.5 amp/dm Temperature: 20 to 60C Rate of deposition at l amp.dm 1 micron in 4 minutes. Intensiveagitation of electrolyte or cathode is effected.

Thiselectrolyte furnishes light yellow, about 20 carat coatings. Thecoatings deposited from this electrolyte are high gloss and tarnishresistant.

EXAMPLE '4 g/liter Potassium dicyanoaurate (l) K(Au(CN)2) 10.0 Ammoniumsulfate (NH SO 50.0 Boric acid H 80 30.0 Ethylene glycol, HOCH CH OH60.0 Palladium cyanide, Pd(CN) 4.5 Nickel sulfate NiSO -7H O 10.0Ethylene diamine tetracetic acid dipotassium salt 12.0 N-( 3-propyll,2-diole )-diethylene triamine, (CH --OHCHOHCH NHCH CH NHCH- 1.0 CH -NHSodium arsenate, Na AsO 0.2 Fonnaldehyde, ("H O 7.5 pH value: 6.5

Applicable current density: from 0.2 to 1.0 amp/dm Temperature: 20 to CThe rate of deposition at l amp/dm is 1 micron in 8 minutes.

This electrolyte furnishes almost white, high-gloss coatings. Thedeposited alloy is approximately 16 carat.

EXAMPLE 5 g/liter Potassium dicyanoaurate (l), K(Au(CN 15.0 Ammoniumsulfate, (NH SO 80.0 Boric acid, H BO 50.0 Ethylene glycol, HOCH CH OH100.0 Cobalt sulfate, CoSo '7H- O 3.0 Nickel sulfate NiSO '7l-l O 2.0lndium sulfate, ln (SO.,);, 0.5 Methyl hydrazine CH -NHNH 0.1 Ethylenediamine tetracetic acid dipotassium salt 6.0 Formaldehyde, CH O 3.0Sodium arsenite, Na;,AsO 0.3

pH value: 5.0

Applicable current density; from 0.1 to 2.5 amp/dm Temperature: 20 to 35C Rate of deposition at 2 amp/dm: 1 micron in 2 minutes According to theinvention an alloy of good electrical properties and excellent abrasivestrength can be deposited with this bath.

The coatings are of high gloss and have a fineness of 23 carat. Thecurrent efficiency is 40 to 60%. The content of alloy metals can begreatly influenced by varying the current density and the speed of goodsor by electrolyte agitation. From a layer thickness of about 5 micronon, a smoothing effect can already be observed.

What is claimed is:

1. An aqueous bath for the electrodeposition of gold or gold alloyshaving a high gloss, said bath having a pH of from about 5 to 10 and anamount of components,-

A, B and C to provide a coating having high gloss and extraordinaryadhesion, said bath comprising A. from about 0.005 to 50 grams per literof at least one compound of the general formula RCHO wherein R isselected from the group consisting of hydrogen, methyl, and the groupCH0, and an aldehyde bisulfite addition compound thereof, and B. fromabout 0.1 to 50 grams per liter of at least one compound of the generalformula R N(R'NR- ),,,--(R),,- NR in which each R is selected from thegroup consisting of hydrogen, alkyl having from 1 to 5 carbon atoms andhydroxy-substituted alkyl having from 1 to 5 carbon atoms, in and n is 0or an integer from 1 to 3, and C. from about 0.001 to 5 grams per literof at least one alkali metal salt of a member of the group consisting ofarsenic acid and arsenious acid, and

D. a water soluble gold compound in an amount of about 1 to 50 grams perliter.

2. A bath adding to claim 1 which contains about ID to 200 grams perliter of boric acid and about to 200 grams per liter of a polyvalentalcohol, the ratio of boric acid to polyvalent alcohol being from aboutlzl to about 1:2, by weight.

3. A bath according to claim 2 wherein the polyvalent alcohol isethylene glycol.

4. A bath according to claim 1 wherein component A is selected from thegroup consisting of formaldehyde, acetaldehyde and glyoxal and componentB is sepounds in amounts of about 0.01 to 200 grams per liter. =l=

1. AN AQUEOUS BATH FOR THE ELECTRODEPOSITION OF GOLD OR GOLD ALLOYSHAVING A HIGH GLOSS, SAID BATH HAVING A PH OF FROM ABOUT 5 TO 10 AND ANAMOUNT OF COMPONENTS, A, B AND C TO PROVIDE A COATING HAVING HIGH GLOSSAND EXTRAORDINARY ADHESION, SAID BATH COMPRISING A. FROM ABOUT 0.005 TO50 GRAMS PER LITER OF AT LEAST ONE COMPOUND OF THE GENERAL FORMULA RCHOWHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, METHYL, ANDTHE GROUP -CHO, AND AN ALDEHYDE BISULFITE ADDITION COMPOUND THEREOF, ANDB. FROM ABOUT 0.1 TO 50 GRAMS PER LITER OF AT LEAST ONE COMPOUND OF THEGENERAL FORMULA R2N-(R''-NR)M-(R'' )N-NR IN WHICH EACH R IS SELECTEDFROM THE GROUP CONSISTING OF HYDROGEN, ALKYL HAVING FROM 1 TO 5 CARBONATOMS AND HYDROXY-SUBSTITUTED ALKYL HAVING FROM 1 TO 5 CARBON ATOMS, MAND N IS 0 OR AN INTEGER FROM 1 TO 3, AND C. FROM ABOUT 0.001 TO 5 GRAMSPER LITER OF AT LEAST ONE ALKALI METAL SALT OF A MEMBER OF THE GROUPCONSISTING OF ARSENIC ACID AND ARSENIOUS ACID, AND D. A WATER SOLUBLEGOLD COMPOUND IN AN AMOUNT OF ABOUT 1 TO 50 GRAMS PER LITER.
 2. A bathadding to claim 1 which contains about 10 to 200 grams per liter ofboric acid and about 10 to 200 grams per liter of a polyvalent alcohol,the ratio of boric acid to polyvalent alcohol being from about 1:1 toabout 1:2, by weight.
 3. A bath according to claim 2 wherein thepolyvalent alcohol is ethylene glycol.
 4. A bath according to claim 1wherein component A is selected from the group consisting offormaldehyde, acetaldehyde and glyoxal and component B is selected fromthe group consisting of hydrazine, methyl hydrazine,N-(3-propyl-1,2-diol)-diethylene triamine, triethylene tetramine andsalts thereof.
 5. A BATH ACCORDING TO CLAIM 1 FOR ELECTRODEPOSITION OFGOLD ALLOY CONTAINING AT LEAST ONE ALLOY METAL SELECTED FROM THE GROUPCONSISTING OF SILVER, COPPER, ZINC, CADMIUM, COBATH, NICKEL, PALLADIUM,INDIUM, MANGANESE, ANTIMONY AND TIN WHEREIN THE ALLOY-METALS ARE ADDEDTO THE BATH IN THE FORM OF WATER-SOLUBLE COMPOUNDS IN AMOUNTS OF ABOUT0.01 TO 200 GRAMS PER LITER.